This invention relates to temperature sensitive capsules, particularly but not exclusively for use as the temperature responsive elements of temperature sensitive electrical switches, that is switches which respond when the temperature to which they are subjected reaches or exceeds a predetermined level.
Our British Patent Specifications Nos. 1509772 (T. M. Jackson-R. J. Hodges 51-25) and 1571754 (T. M. Jackson-R. J. Hodges 58-34) describe such switches. The switches essentially comprise a capsule, closed at one end by a domed or bowed disc having a flip-over characteristic, and containing a quantity of suitable gas or liquid which, on expanding due to a temperature rise, causes the disk to deflect and operate a set of electrical contacts.
In order to improve the performance or characteristics of these known basic switches or other similar switches employing such capsules various modifications to the capsule thereof are now proposed.
According to one aspect of the present invention there is provided a capsule, for use as a temperature responsive element, comprising a sealed enclosure containing a liquid or gas, one wall of the enclosure being a bowed disc, wherein when the temperature to which the capsule is subjected passes through a predetermined value the vapour pressure within the enclosure changes in such a way as to cause the bowed disc to change from a concave state to a convex state, or vice versa, and wherein the disc is manufactured from precipitation hardened stainless steel or precipitation hardened beryllium copper.
According to another aspect of the present invention there is provided a capsule, for use as a temperature responsive element, comprising a sealed enclosure containing a liquid, one wall of the enclosure being a bowed disc, wherein when the temperature to which the capsule is subjected passes through a predetermined value the vapour pressure within the enclosure changes in such a way as to cause the bowed disc to change from a concave state to a convex state, or vice versa, wherein the capsule is filled with a minimum amount of the liquid such that the capsule operates normally in a logarithmic mode up to the limit of saturated vapour but such that in the event of overtemperature the filling behaves like a gas and obeys gas laws whereby to reduce the rate of pressure increase with temperature within the capsule.
According to a further aspect of the present invention there is provided a method of adjusting the operate temperature of a capsule, for use as a temperature responsive element, to a predetermined value, which capsule comprises a sealed enclosure containing a liquid or gas and such that when the temperature to which the capsule is subjected passes through a certain value, the operate temperature, the vapour pressure within the enclosure changes in such a way as to cause a bowed wall forming one wall of the enclosure to change from a concave state to a convex state, which method comprises reducing the internal volume of the enclosure, by permanently deforming another wall of the enclosure, to a volume value at which the bowed disc will change state when the enclosure is heated at the predetermined value.
According to yet another aspect of the present invention there is provided a method of adjusting the release temperature of a capsule, for use as a temperature responsive element, to a predetermined value, which capsule comprises a sealed enclosure containing a liquid or gas and such that when the temperature the capsule is subjected to passes through a certain value, the release temperature, the vapour pressure within the enclosure changes in such a way as to cause a bowed disc forming one wall of the enclosure to change from a convex to a concave state, the disc being connected to a cylindrical can member, closed at one end and forming the remaining walls of the enclosure, at the end opposite the one end by means of a flange initially extending in a first direction radially outwards with respect to the axis of the cylinder, which method comprises permanently distorting the flange to extend at such an angle to the first direction whereby the disc is biased to change between the convex and concave states when the capsule is heated at the predetermined release temperature value.